500 light years away, in the constellation of Cygnus, orbiting a dwarf star, lies the planet Kepler-186f.
It’s too small to be seen by even the most powerful telescope. But every time it passes in front of the star it orbits, the planet dims the light from the star by a tiny amount. Incredibly, from three thousand trillion miles away, NASA’s Kepler spacecraft is able to measure this. Work out how much the star dims, and how often, and the existence, size and distance of the orbiting planet can be calculated.
But in 2014, when astronomers ran the figures on Kepler-186f, they found something unusual. They had discovered the very first earth-sized planet anywhere else in the galaxy to be located in the ‘habitable zone’ where life can exist.
Liquid water is the crucial ingredient. Too close to the star, where it’s too hot, and water just boils away. Too far away, where it’s too cold, and it freezes. To have life, you need water, and to have water, a planet has to be, in the words of Goldilocks, ‘not too hot, not too cold, but just right.’ Hence talk in popular science writing of ‘the Goldilocks zone’ or even ‘a Goldilocks planet’: one that is ‘just right’ for life.
Of course, more is needed. As yet, astronomers can’t tell if Kepler-186f has an atmosphere, or what it’s made of. The next generation of telescopes may answer these questions. But if there is extra-terrestrial life out there in the galaxy, Kepler-186f is the most likely bet so far.
The existence of planets like Kepler-186f should be no surprise. If there are billions of stars in the universe, orbited by billions of planets, some of those planets are bound to be in the zone where life could exist. Goldilocks planets are a statistical inevitability.
Curiously, however, some scientists also talk about us living in a Goldilocks universe. The bigger conundrum is this. Why is the universe as a whole capable of supporting life? Why does the universe give rise to habitable zones?
There’s no logical reason it should. As the Astronomer Royal Martin Rees points out, the universe is governed by all sorts of physical constants, which could easily be different. Tweak them even a little, and life becomes impossible.
Change the gravitational settings at the Big Bang, for instance, and the universe either contracts right back on itself, or flies apart without ever allowing stars and planets to form. Adjust the forces which hold the atom together even just a tad, and suddenly the chemicals needed for life become impossible.
Numerous physical constants in the universe seem to be fixed just so. Not too big, not too small, but just right. The universe, it seems, is finely-tuned for life. But why?
‘A common sense interpretation of these facts’, declared British astronomer (and atheist) Fred Hoyle, ‘suggests that a superintellect has monkeyed with physics.’ God, in other words, is at work.
Nonsense, say the sceptics. There could be billions of possible universes. Some are bound to allow the evolution of life. There’s nothing surprising here at all. It’s just a matter of statistics.
Away from the noise and light pollution of the city, we stare at the stars, and wonder at the beauty of the night sky. Astonishingly, and only as a result of very precise conditions, the universe supports life. The odds against it are staggering. And there’s no scientific reason why.
Evidence for intelligent design? Or did we just get lucky?